| The amount of blast furnace dust(BF dust)emission increases year by year with the increase of iron and steel production in China.In iron and steel making plant,the main method to deal with the BF dust is returning it to the sintering process,but the zinc contained in the dust will accumulate and do harm to the stable operation of the blast furnace.Hence,it is important to separate zinc and iron in BF dust to realize the comprehensive utilization of resources.In addition,zinc ferrite is inevitably formed in blast furnace,which has stable structure and is difficult to be dissolved by common leaching method,resulting in low leaching rate of zinc and waste of zinc resource when zinc was retained in the leaching residue.Therefore,the zinc-bearing blast furnace dust was treated by pyro-hydrometallurgical complex process in this thesis.The insoluble zinc ferrite in blast furnace dust was converted into soluble zinc sulfate by sulfate roasting process,and then the separation of zinc and iron was realized by dilute acid leaching of the calcine.The element content,phase composition and morphology of the raw material,calcine and residue were analyzed by X ray diffraction fluorescence spectrometer(XRF),X ray diffractometer(XRD),scanning electron microscope(SEM)and Energy dispersive spectrometer(EDS).The thermodynamic data of the reactions related to the sulfate roasting process were calculated by Factsage software,and the diagram for predominance of Zn-Fe-S-O system was drawn.The thermodynamic conditions of the reactions were analyzed,and the temperature range of the sulfate roasting of blast furnace dust was determined to be500-730?.The effects of such parameters as roasting temperature,roasting time and weight ratio of ferric sulfate to BF dust on the leaching rate of zinc and iron were studied.The results when blast furnace dust was firstly roasted at the roasting temperature of 600?,roasting time of 1 h and weight ratio of ferric sulfate to BF dust of 1.2:1,then the calcine was leached by sulfuric acid,the leaching rate of zincreaches84.37%.The effects of sulfuric acid concentration,leaching temperature,leaching time and liquid-solid ratio on the leaching rate of zinc and iron in roasted products were studied.The results show that sulfuric acid concentration and leaching temperature are the main factors affecting the leaching rate of zinc and iron.Under the conditions of leaching acidity 110 g/L,liquid-solid ratio 10:1,leaching time 1 h and leaching temperature80?,the leaching rate of zinc and iron in sulfated roasting products of BF dust is84.37% and 24.59% respectively.The leaching kinetics of zinc from sulfate roasting products of BF dust was studied by diffusion theory.The effects of leaching temperature a nd sulfuric acid concentration on the reaction rate were investigated.The results show that the kinetic s of the leaching process belongs to the "unreacted nucleus reduction" model with no solid product layer formed.The leaching kinetic equation is 1-2/3R-(1-R)2/3= kt.The apparent activation energy of leaching reaction was calculated to be17.4 k J/mol.The leaching process is controlled by internal diffusion process.Hence increasing reaction temperature and sulfuric acid concentration can accelerate zinc leaching process and increase zinc leaching rate. |
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